Valley-detection device for quasi-resonance switching and method using the same
a detection device and quasi-resonance technology, applied in the field of valve detection technology, can solve the problems of low manufacturing cost, inability to predict the capacitive loss of the mosfet during the switch turn-on transition, and inability to minimize the capacitive loss of the mosfet, so as to achieve the effect of reducing the switching power loss
Active Publication Date: 2014-02-25
SYNC POWER CORP
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AI Technical Summary
Benefits of technology
Precise detection of valley voltage and time points reduces switching power loss by optimizing the switching timing, enhancing efficiency in power converter circuits.
Problems solved by technology
It can implement isolated switching mode power supplies (SMPS) with one switching component and one transformer resulting in low manufacturing cost.
However, the switching losses are unavoidable in hard-switching mode.
So the capacitive loss of the MOSFET during switch turn-on transition cannot be predicted and minimized.
Method used
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[0021]The present invention provides a valley-detection device for quasi-resonance switching and a method using the same which reduces switching power loss. The reason related to the method is introduced as below.
[0022]Refer to FIG. 1 and FIG. 2. When the transistor is turned on, the VDS voltage is a grounding voltage. When the transistor is turned off and after the transformer energy is fully discharged, a resonant signal is generated across the drain and the source. The resonant signal is a sine wave signal whose voltage oscillates around a mid-level, and is hereby referred to as a high voltage VH. In other words, the voltage of the resonant signal is gradually close to the high voltage VH. The voltage of the resonant signal begins to drop from a voltage Vhigh corresponding to a start time point, wherein the voltage Vhigh is larger than the high voltage VH. When the voltage of the resonant signal first reaches the high voltage VH, the present time is defined as a crossing time poi...
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A valley-detection device for quasi-resonance switching and a method using the same is disclosed, which uses first and second capacitors to connect with a comparator, and the comparator connects with an NMOSFET connecting to a transformer. When the NMOSFET is turned off, the energy stored in the transformer is discharged and a resonant signal across the source and the drain is generated, and a first constant current charges the first capacitor at a start time point of the resonant signal until a voltage of the resonant signal first reaches to a crossing voltage. Then, a second constant current charges the second capacitor when the voltage of the resonant signal equals to the crossing voltage while the voltage of the resonant signal varies from high to low. Finally, the comparator turns on the NMOSFET when a voltage of the second capacitor equals to a voltage of the first capacitor.
Description
BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a valley-detection technology, particularly to a valley-detection device for quasi-resonance switching and a method using the same.[0003]2. Description of the Related Art[0004]Flyback is one of the most popular topologies in medium and low power applications due to its simplicity. It can implement isolated switching mode power supplies (SMPS) with one switching component and one transformer resulting in low manufacturing cost. However, the switching losses are unavoidable in hard-switching mode.[0005]As shown in FIG. 1 and FIG. 2, a power converter circuit includes a transformer 10 having a primary winding PW and a secondary winding SW and an N-channel metal oxide semiconductor field effect transistor (NMOSFET) 12 connected to the primary winding PW. An input high voltage VH is applied to the primary winding PW. A voltage VG is periodically applied (TON) to the gate of the NMOSFET 12 to ...
Claims
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IPC IPC(8): H02M3/335
CPCY02B70/1433Y02B70/1491H02M3/33523H02M2001/0054Y02B70/10H02M1/0054
InventorTSUI, CHENG-WEN
OwnerSYNC POWER CORP